Arrangement for pumping an anisotropic laser crystal

Abstract

The object in an arrangement for pumping an anisotropic laser crystal is to reduce the influence of the destruction limit of the laser crystal on increased pump power density and, in this connection, to achieve improved beam quality and increased efficiency of a diode-pumped solid state laser. At the same time, the pump volume and cross-sectional area are to be kept as small as possible along a length of the crystal corresponding at least approximately to the absorption length. The arrangement operates with an asymmetric pump beam whose pump beam cross section has different dimensions perpendicular to one another and with a laser beam cross section which is adapted to this asymmetry. That axis of the crystallographic axes of the anisotropic laser crystal in whose direction the highest value of the crystal breaking limit exists is oriented along the greatest temperature gradient in the direction of the smaller dimension of the pump beam cross section.

1. An arrangement for pumping an anisotropic laser crystal comprising:
 a pump radiation source for generating a pump beam with an asymmetrical cross section having a smaller dimension in a first direction and a larger dimension in a second direction, said first and second directions being perpendicular to one another;  
 said anisotropic laser crystal having a first and a second crystallographic axis perpendicular to one another, each axis having a different crystal breaking limit and a different thermal coefficient of expansion;  
 wherein in the direction of the first crystallographic axis said anisotropic laser crystal has a greater crystal breaking limit in comparison to the second crystallographic axis of said anisotropic laser crystal with a smaller crystal breaking limit and which second crystallographic axis of said anisotropic laser crystal has a smaller thermal coefficient of expansion than the first crystallographic axis of said anisotropic laser crystal;  
 wherein said anisotropic laser crystal is oriented with said first crystallographic axis in the first direction of the smaller dimension of the pump beam asymmetrical cross section.  
 
   
   
     2. The arrangement according to  claim 1 , wherein the anisotropic laser crystal having a crystal cross section which is penetrated by the pump beam,
 said crystal cross section having a smaller dimension in the first direction of the pump beam asymmetrical cross section that in the second direction of the pump beam asymmetrical cross section.  
 
   
   
     3. The arrangement according to  claim 2 , wherein due to the direction-dependent differences in the strengths of the thermal lens there is a laser beam cross section in the laser crystal whose axial ratio is greater than 1:1 and less than 1:3 in directions extending perpendicular to one another. 
   
   
     4. The arrangement according to  claim 3 , wherein said anisotropic laser crystal is an Nd:YVO 4  crystal. 
   
   
     5. The arrangement according to  claim 4 , wherein the pump radiation is adapted to an elliptic beam cross section by means of two cylindrical lenses. 
   
   
     6. The arrangement according to  claim 1 , wherein the laser crystal has a Brewster surface as beam outlet surface and the axial ratio is increased by the factor of the ratio of the index of refraction of the laser crystal to the index of refraction of air. 
   
   
     7. The arrangement according to  claim 6 , wherein said pump radiation source being a diode laser with a line-shaped arrangement of individual emitters emitting beam bundles,
 said diode laser having a fast-axis and slow-axis which coincide with the first and the second direction of the pump beam asymmetrical cross section respectively, and collimating the pump beam in the direction of the fast-axis and slow-axis,  
 wherein the collimator for collimating the pump beam in the direction of the slow-axis comprises individual lenses which are arranged in a plane of the beam intersection of the beam bundles emitted by the individual emitters.  
 
   
   
     8. The arrangement according to  claim 6 , wherein the pump radiation has a defined divergence in the fast-axis direction and focusing is carried out by means of an aspheric lens.